#!/usr/bin/python

num = input("please input you num:")
if num.isdigit():
    if (int(num) >= 90 and int(num) <=100):
        print("A")
    elif (int(num) >= 80 and int(num) <=89):
        print("B")
    elif (int(num) >= 70 and int(num) <=79):
        print("C")
    else:
        print("D")
else:
    print("please input you 0-100 num") 
